Typically Jenkins is used with a pool of builders. You may need to ask whoever set it up.
You can also check the 'Console Output' on a Jenkins job, and on the upper left you can click something like 'Show all', and then the beginning of that console log should say what builder that job ran on. I don't have access to our Jenkins right now but I think that's the way.
So ultimately what I'm saying is that if you have multiple builders you need to set each one up. If you install ideviceinstaller on one of the builders and Jenkins uses a different builder to run the job, you would get an error like you describe.